Contact screen



June 1966 A. RIEMERSCHMID ETAL 3,2

CONTACT SCREEN 2 Sheets-Sheet 1 Filed May 31, 1963 PRIOR. ART

J1me 1966 A. RIEMERSCHMID ETAL 3,

CONTACT SCREEN Filed May 31, 1963 2 Sheets-Sheet 2 'm 5 /\xnI F i ll&\\\\\\\\\\\\V l -14 United States Patent 3,258,341 CONTAGI SCREEN AntonRiemerschmid, 54 Zillestrasse, and Wilhelm Eclrerlin, 12-14 AmWeingarten, both of Frankfurt, Germany Fiied May 31, 1963,5612 No.284,491 12 Claims. (Cl. 96-116) This application is acontinuation-in-part of our earlier application, Serial No. 591,074,filed June 13, 1956, and now abandoned.

This invention relates to contact screens.

It is an object of the invention to provide an improved contact screen.

It is a further object of the application to provide a universal ormulti-purpose contact screen which may be used with equal facility inconnection with offset and engraving techniques.

It is a further object of the invention to provide an improved contactscreen which provides for reproductions of the highest quality.

Yet another object of the invention is to provide an improved contactscreen wherein all tone ranges of an original are faithfully reproducedwith substantially no tone distortion.

Still another object of the invention is to provide an improved contactscreen which is independent of the density thereof.

A still further object of the invention is to provide an improvedcontact screen which permits a normal preexposure without the occurrenceof tone flattening.

Yet another object of the invention is to provide an improved contactscreen wherein contrasts may be increased or decreased with equalsuccess.

In achieving the above and other of its objectives, the inventioncontemplates the provision of a contact screen comprising asubstantially transparent sheet with a surface layer positioned thereon.

The surface layer is provided with perpendicularly disposed lineararrays of evenly spaced substantially opaque dots according to apreferred embodiment. Each group of four adjacent of the dots forms thevertices of a right quadrilateral from which all other of these opaquedots are excluded.

According to the preferred embodiment, the surface layer furtherincludes a gradually varying grey tone portion extending from eachopaque dot towards each dot adjacent thereto. Each grey tone portiondiminishes to a minimum opacity zone midway between each opaque dot andthe corresponding adjacent dot.

In accordance with a feature of the invention, the minimum opacity zonesare in right quadrilateral alignments about respective of the opaquedots, the right quadrilateral alignments constituting the perimeters ofvarying opacity zones in which the opaque dots are centered.

Still further, the surface layer is provided with semitransparent zoneslocated at the vertices of the right quadrilateral alignments of theminimum opacity zones, the semi-transparent zones being located inperpendicular linear arrays.

In accordance with a further feature of the invention, the surface layeris further provided with substantially fully transparent dots centrallylocated in the semi-transparent zones.

According to yet another feature of the invention, the semi-transparentzones have about .5 to the opacity of the opaque dots and the minimumopacity zones extend radially from the semi-transparent zones and haveno more than about less opacity than the semi-transparent zones.

According to still another feature of the invention, the

areas of the semi-transparent zones have a ratio to the 3,258,34lPatented June 28, 1966 "ice FIGURE 1 is a plan view of a contact screenin accordance with the prior art;

FIGURE 2 is a plan view of a section of a contact screen provided inaccordance with the invention;

FIGURE 3 is a pictorial representation of a microphotograph of thecontact screen of FIG. 2, with light exposed through the same androtated 45 relative to the showing of FIG. 2;

FIGURE 4 is a view similar to that of FIG. 2, illustrating the dotgrowth pattern of this screen;

FIGURE 5 is a view similar to FIG. 1, showing the dot growth pattern ofthe prior art contact screen;

FIGURE 6 is an enlarged view of the contact screen of the invention;

FIGURE 7 is a further enlarged view of a contact screen of theinvention;

IISYIGURE 8 is a cross-section along line VIIIVIII of F 7;

FIGURE 9 illustrates a dot configuration permissible in accordance withthe invention;

FIGURE 10 illustrates a further dot configuration permissible inaccordance with the invention;

FIGURE 1,1 is an enlarged view of a contact screen provided inaccordance with the invention, the details thereof being illustrateddiagrammatically;

FIGURE 12 is a cross-sectional view taken along line XIIXII of FIG. 11;

FIGURE 13 is a cross-sectional view taken along line XIII-XIII of FIG.11; and

FIGURE 14 is a cross-sectional view taken along line XIVXIV of FIG. 11.

Contact screens may be classified according to the arrangement of thedots in the screen. On this basis, two broad groups of screens may bedesignated, the one based on a checker board arrangement, the other on aso-called in-line arrangement of the invention.

The arrangement of the dots in the screen which follows the checkerboard pattern is shown in FIGURE 1. It will be noted that on a givenline, each screen dot 20 is separated by an empty space, and that thelines of the dots above and below the given line follow the same orderbut are offset by one dot. This gives the familiar appearance of theconventional checker board pattern. The contact screens comprising thisgroup are the singlepurpose, offset-only and engraving-only screens.

The arrangement of the dots in the screens which follow the in-linepattern is the basis for the second group. This is designated themulti-purpose type and is shown in FIG. 2. It will be noted that on agiven line of dots 22 in the screen, the dots are adjacent one anotherand follow each other in order. The line of dots above and below thegiven line are identical, and are all in-line, one above the other allthe way through. A reproduction of a micro-photograph of themulti-purpose screen is shown in FIG. 3. Some further characteristicfeatures which cannot be reproduced photographically will be fouradjacent opaque dots, initial exposure of light passing through thisarea, results in tiny pin-point dots. Continued exposure of lightresults in the formation of progressively larger dots, which enlargewith exposure, the direction of growth occurring along the diagonals ofa rectangle, until larger dots on a checker board pattern is formed.During the exposure, the dot structure of the screen is turned intoanother dot structure in the screened negative, or positive. As shown inFIG. 4 all the dots turned into a checker board pattern run in the angleof 45 to the border of the screened negative or positive.

In FIG. of the drawings a similar dot growth pattern is shown, but thedirection of the growth pattern is horizontally and vertically in thescreened negative or positive.

Because of the density gradation of the dot in the screen, growth of thedot in the screened result is gradual, the end point being areproduction of the tones of the copy, within the limits of thecharacteristics of the screen.

The multi-purpose screen may cover, for example, a density range of 1.6,i.e., from about .35 to about 1.95. Thus, the screen will give ahalftone copy of this tonal range without need of flash exposure, Forcopy having a density range exceeding that of the screen, a flashexposure is used.

An interesting characteristic of the multi-purpose screen is indicatedin the location of the middle tone values in the halftone when flashexposure is used. This may be illustrated by the following: If a tenstep gray scale is photographed through the multi-purpose screen,without flash exposure, a slightly less than 50% dot is observed in thefifth step, and a slightly greater than 50% dot is observed in the sixthstep. If normal flash exposures are used, together with the mainexposure, this condition still prevails, and the exact middle tones showup essentially as 50% dots in 'the center of the gray scale, where theyreally belong. Flash exposures with the checkerboard type of screen,however, are observed to shift the 50% dots away from the center of thegray scale.

Another interesting characteristic of the multi-purpose screen lies inthe fact that the tone reproduction quality is unaffected by the densityof the screen. A lighter screen merely shoots faster. If a processcamera or enlarger is used, this feature permits short exposures. On theother hand, if'one attempts to use a low density screen in a contactframe, working control of the exposures becomes diflicult. Consequently,the multi-purpose screen is furnished in a medium density which allowsfast exposures in the camera, and provides reasonable control if thesame screen should be used in a contact frame.

Other features of the multi-purpose screen worthy of mention include:

(1) Because of the density gradient in the screendot, and the proportionof light to dark in the screen itself, this type of screen may be usedinterchangeably for producing both high contrast offset type negatives,and low contrast engraving type negatives, as desired.

(2) Since the screen is transparent, like the glass crossline screen, itcan be used to produce screened negatives from colored copy for blackand white production, and for direct, color separation work in the shortrun process.

(3) The density range coverage of the screen is high, approximately 1.6.

Referring next to FIGS. 6 and 7, two enlarged views of a portion of acontact screen such as that illustrated in FIGS. 2 and 4 are shown. Toprovide for correlation with FIGS. 2 and 4, a dot 22 is indicated.

In the contact screen of the invention, a plurality of substantiallyopaque dots are employed, preferably in rectilinear arrays which areperpendicularly disposed to one another, the opaque dots being evenlyspaced therein.

In FIG. 6 four opaque dots 24, 26, 28 and are illustrated. These will beconsidered to constitute a group ofv four adjacent opaque dots whichform the verticcs of a right quadrilateral (in this case a square) fromwhich all other of the opaque dots are excluded.

In this right quadrilateral alignment, for example, opaque dot 24 willbe considered to be adjacent opaque dots 26 and 30, but not adjacentopaque dot 28, whereas opaque dot 26 will be considered as beingadjacent opaque dots 24 and 28, but not adjacent opaque dot 39, andsoon.

In FIGS. 6 and 7 it will be further noted that each opaque dot issurrounded by a gradually varying grey tone portion extending from eachopaque dot towards each dot adjacent thereto.

It will be moreover noted that each grey tone portion diminishes to amini-mum opacity zone midway between each opaque dot and thecorresponding adjacent dot.

It is to be noted that the minimum opacity zones are arranged in rightquadrilateral alignments about respective of said opaque dots. Forexample, minimum opacity zones 32, 34, and 38 are three sides of asquare encompassing the associated opaque dot. It may therefore be saidthat the right quadrilateral alignments of the-rninimum opacity zonesconstitute the perimeters of varying opacity zones in which the opaquedot-s are centered.

From the drawing it will appear that the preferred form of the surfacelayer to form the zones of varying capacity is that of a multitude ofpyramids, the upper vertice of which constitutes the opaque dot. This isshown more graphically in'the cross-sectional view which appears in FIG.8, wherein the transparent layer 40 may be seen along with the coveringor surface layer 42 formed of a material affording suitable opacity inaccordance with its thickness. In FIG. 8 it will be seen that the greytone is gradually varying rather than a step-by-step variation so thatit will be clear that the increments indicated in FIGS. 6 and 7 are forillustration purposes only.

The shapes of the opaque dots, as well as the dots 22 (as will bedescribed in greater detail hereinafter) may be square, as seen in FIGS.6 and 7, or polygonal as shown in FIG. 9, or even star-shaped as shownin FIG. 10. Other configurations are also possible Within [the scope ofthe invention.

Reference is next made to FIG. ll wherein the separate zones and areascontemplated in accordance with the in'vention are illustrated as beingsharply delineated from one another. It will be appreciated, however,that in practice the different areas and zones merge into one anotherrather than having sharp lines of demarcation therebetween. The purposeof showing sharp lines of demarcation between the different zones is toenable a definition of the invention which will facilitate the usethereof by those skilled in the art.

Referring to FIG. 11, a substantially opaque dot 44 is shown, surroundedby four zones 46, 48, 50 and 52. Opaque dot 44 corresponds to the opaquedots 24, 26, 28 and 30 of FIG. 6 and zones 46, 48, 50 and 52 correspondto the dots 22 to which reference has heretofore been made.

Also illustrated are zones of minimum opacity 53, 54, 56 and 58, thesezones also corresponding to the zones of minimum opacity to whichreference has previously been made.

From FIG. 11 it will be seen that, as indicated above, said zones ofminimum opacity which extend radially from respective of zones 46, 48,50 and 52, cooperatively constitute the perimeter of a varying opacityzone 60, constituted by the above-noted pyramidal variations in thesurface layer.

It will now appear that the zones 46, 48, 50 and 52 are comprised of twoseparate and distinct parts. Retferring, for example, to the zone 46, itwill now appear that this comprises a semi-transparent zone 62, in whichis centrally located a substantially fully transparent pinpoint dot orspot 64.

With reference to FIG. 12, it will be seen that surface layer 42 locatedon transparent sheet 40 has a particular profile to provide for theaforegoing.

More particularly, the substantially fully transparent dot appears alongsection line XII-XII of FIG. 11, as

portion 64' in the surface layer 42, which portion representssubstantially the absence of the surface layer 42 at this point.

Still further it will be seen that the semi-transparent zone appearsalong section line XIIXII as indicated at 62', the zone of mini-mumopacity appearing between adjacent of the opaque dots appearing in FIG.12 as shown at 58.

The opaque dots, semi-transparent zones and zones of minimum opacityhave a preferred physical relationship. More particularly, thesemi-transparent zones have about .5 to 5% the opacity of the opaquedots, such as the dot 44. The zones 64' (see also dot 64) are preferablyalmost fully transparent. The minimum opacity zones (e.g., zone 58) haveno more than about 10% less olpacity than the semi-transparent zones.

The relationship of the opaque dots, zones of varying grey tone, thesemi-transparent zones and the fully trainsparent spots is apparent fromthe cross-section given in FIG. 13, it being understood that therelative sizes shown in the drawing are not in correct proportion.

In FIG. 13 the opaque spot 44 is shown as being constituted by the peakof the associated pyramid or zone of varying opacity 60. Associatedtherewith are the semitransparent zones 62" and 62". Also seen inconnection with FIG. 13 are the pin point spots of full transparency,such as indicated at 64' and 64". The relationship of the aforenotedpyramids and opaque dots to the associated zones of minimum transparencyis apparent from FIG. 14, wherein are illustrated zones 53 and 56 ofminimum opacity, located midway between opaque dot 44 and the adjacentof the opaque dots (not shown).

The specific lines of demarcation illustrated in FIG. 11 are intendedfor purposes of enabling the definition of the areas of the respectivezones.

In this regard, the-preferred embodiment of the invention provides thatthe area of a semi-transparent zoneto the area of a varying opacity zoneis in the order of about 1:5 0 to 1:400. More particularly and by way ofexample,

the area of zone 62 to the area of zone 60 is in the range of from about1:50 to 1:400.

A still further characteristic feature of the invention, which isbelieved essential to the practice thereof, involves a particularrelationship between the area of the fully transparent dots to theassociated semi-transparent zones. Thus, the area of fully transparentspot 64 to semi-transparent zone 62 is in the range of from about 1:20to 1:60.

By Way of review, the invention contemplates that the above contactscreen is a multipurpose contact screen adapted for use with both offsetand letterpress techniques and that reproductions of the highest qualityare obtained with such screens with all tone ranges of an original beingfaithfully reproduced with no tone distortion. Moreover, contact screensprovided with the aforenoted features are independent of the density ofthe surface layer thereon. Still further, with a normal pre-exposurestep, no tone flattening will occur with contact screens of theinvention. Still further, contrasts may be increased or decreased withequal success in employing contact screens of the invention. 1

There will now be obvious to those skilled in the ant many modificationsand variations of the structure set forth 'above. These modificationsand variations will not depart lfIOII]. the scope of the invention asdefined by the following claims.

What is claimed is:

1. A contact screen comprising a substantially trans-.

6 surface layer further having semi-transparent zones distributed aboutthe opaque dots and located between said minimum opacity zones, saidsurface layer further having substantially fully transparent spotslocated in the semi-transparent zones, said semi-transparent zoneshaving about .5 to 5% the opacity of said opaque dots, the area of eachtransparent spot to the area of the associated semi-transparent zonebeing about 1:20 to 1:60.

2. A contact screen comprising a substantially transparent sheet and asurface layer on said sheet, said surface layer having arrays of spaced,substantially opaque dots, each group of four adjacent of said dotsforming the vertices of a quadrilateral from which all other of saidopaque dots are excluded, said surface layer including a graduallyvarying grey tone portion extending from each opaque dot towards eachdot adjacent thereto, each grey tone portion diminishing to a minimumopacity zone between each opaque dot and the corresponding adjacent dot,the minimum opacity zones constituting the perimeters of varying opacityzones constituted by the varying grey tone portions and in which theopaque dots are centered, said surface layer further havingsemi-transparent zones located in the minimum opacity zones, saidsurface layer further having substantially fully transparent spotslocated in the semi-transparent zones, said semi-transparent zoneshaving about .5 to 5% the opacity of said opaque dots, the areas of saidsemi-transparent arcashaving a ratio to the areas of said varyingopacity zones of about 1:50 to 1:400, the area of each transparent spotto the area of the associated semi-transparent zone being about 1:20 to1:60.

3. A contact screen comprising a substantially transparent sheet and asurface layer on said sheet, said surface layer having perpendicularlinear arrays of evenly spaced, substantially opaque dots, each group offour adjacent of said dots forming the vertices of a right quadrilateralfrom which all other of said opaque dots are excluded, said surfacelayer including a gradually varying grey tone portion extending fromeach opaque dot towards each dot adjacent thereto, each grey toneportion diminishing to a minimum opacity zone midway between each opaquedot and the corresponding adjacent dot, the minimum opacity zones beingin right quadrilateral alignments about respective said opaque dots,said right quadrilateral alignments constituting the perimeters ofvarying opacity zones in which the opaque dots are centered, saidsurface layer further having semitransparent zones located at thevertices of the rectilinear alignments of said minimum opacity zones,said semitransparent zones being located in perpendicular linear arrays,said surface layer further having substantially fully transparent spotscentrally located in the semi-transparent zones, the areasof saidsemi-transparent areas being substantially less than the areas of saidvarying opacity zones, the area of each transparent spot beingsubstantially less than the area of the associated semi- 'transparentzone.

4. A contact screen comprising a substantially transparent sheet and asurface layer on said sheet, said surface layer having perpendicularlinear arrays of evenly spaced, substantially opaque dots, each group offour adjacent of said dots forming the vertices of a right quadrilateralfrom which all other of said opaque dots are excluded, said surfacelayer including a gradually varying grey tone portion extending fromeach opaque dot'towards each dot adjacent thereto, each grey toneportion diminishing to a minimum opacity zone midway between each opaquedot and the corresponding adjacent dot, the minimum opacity zones beingin right quadrilateral alignments about respective said opaque dots,said right quadrilateral alignments constituting the perimeters ofvarying opacity zones in which the opaque dots are centered, saidsurface layer further having semi-transparent zones located at thevertices of the rectilinear alignments of said minimum opacityzonesfsaid semi-transparent zones being located in perpendicular lineararrays, said surface layer further having substantially fullytransparent spots centrally located in the semi-transparent zones, saidsemi-transparent zones having about .5 to the opacity of said opaquedots, said minimum opacity zones extending radially from thesemi-transparent zones and having no more than about 10% less opacitythan the semi-transparent zones, the areas of said semi-transparentareas being substantially less than the areas of said varying opacityzones, the area of each transparent spot being substantially less thanthe area of the associated semi-transparent zone.

5. A contact screen comprising .a substantially transparent sheet and asurface layer on said sheet, said surface I layer having perpendicularlinear arrays of evenly spaced,

substantially opaque dots, each group of four adjacent of said dotsforming the vertices of a right quadrilateral from which all other ofsaid opaque dots are excluded, said surface layer including a graduallyvarying grey tone portion extending from each opaque dot towards eachdot adjacent thereto, each grey tone portion diminishing to a minimumopacity zone midway between each opaque dot and the correspondingadjacent dot, the minimum opacity zones being in right quadrilateralalignments about respective said opaque dots, said right quadrilateralalignments constituting the perimeters of varying opacity zones in whichthe opaque dots are centered, said surface layer further havingsemi-transparent zones located at the vertices of the quadrilateralalignments of said minimum opacity zones, said semi-transparent zonesbeing located in perpendicular linear arrays, said surface layer furtherhaving substantially fully transparent spots centrally located in thesemi-transparent zones, the areas of said semi-transparent zones havinga ratio to the areas of said varying opacity zones of about 1:50 to1:400, the area of each transparent spot to the area of the associatedsemi-transparent zone being about 1:20 to 1:60.

6. A contact screen comprising a substantially transparent sheet and asurface layer on said sheet, said surface layer having perpendicularlinear arrays of evenly spaced, substantially opaque dots, each group offour adjacent of said dots forming the vertices of a right quadrilateralfrom which all other of said opaque dots are excluded, said surfacelayer including a gradually varying grey tone portion extending fromeach opaque dot towards each dot adjacent thereto, each grey toneportion diminishing to a minimum opacity zone midway between each opaquedot and the corresponding adjacent dot, the minimum opacity zones beingin right quadrilateral alignments about respective said opaque dots,said right quadrilateral alignments constituting the perimeters ofvarying opacity zones in which the opaque dots are centered, saidsurface layer further having semi-transparent zones located at thevertices of the quadrilateral alignments of said minimum opacity zones,said semitransparent zones being located in perpendicular linear arrays,said surface layer further having substantially fully transparent spotscentrally located in the semitransparent zones, said semi-transparentzones having about .5 to 5% the opacity of said opaque dots, the areasof said semi-transparent zones having a ratio to the areas of saidvarying opacity zones of about 1:50 to 1:400, the area of eachtransparent spot to the area of the associated semi-transparent zonebeing about 1:20 to 1:60.

7. A contact screen adapted for use with letterpress and offset printingtechniques comprising a substantially transparent sheet and a surfacelayer on said sheet, said surface layer having perpendicular lineararrays of evenly spaced, substantially opaque dots, each group of fouradjacent of said dots forming the vertices of a right quadrilateral fromwhich all other of said opaque dots are excluded, said surface layerincluding a gradually varying grey tone portion extending from eachopaque dot towards each dot adjacent thereto, each grey tone portiondiminishing to a minimum opacity zone midway between each opaque dot andthe corresponding adjacent dot, the minimum opacity zones being in rightquadrilateral alignments about respective said opaque dots, said rightquadrilateral alignments constituting the perimete'rs of varying opacityzones in' which the opaque dots are centered, said surface layer furtherhaving semi-transparent zones located at the vertices of thequadrilateral alignments of said minimum opacity zones, saidsemitransparent zones being located in perpendicular linear arrays, saidsurface layer further having substantially fully transparent spotscentrally located in the semitransparent zones, said semi-transparentzone-s having about .5 to 5% the opacity of said opaque dots, saidminimum opacity zones extending radially from the semitransparent zonesand having no more than about 10% less opacity than'the semi-transparentzones, the areas of said semi-transparent zones having a ratio to theareas of said varying opacity zones of about 1:50 to 1:400, the area ofeach transparent spot to the area of the associated semi-transparentzone beingabout 1:20 to 1:60.

8. A screen as claimed in claim 7 wherein the varying opacity zones arepyramidal in shape.

9. A screen as claimed in claim 7 wherein said sheet is a rig-htquadrilateral and the linear arrays are arranged at 45 to the sides ofthe sheet.

10. A screen as claimed in claim 7 wherein the dots are quadrilateral.

.11. A screen as claimed in claim 7 wherein the dotsare polygonal.

12. A screen as claimed in claim 7 wherein the dots are star-shaped.

References Cited by the Examiner UNITED STATES PATENTS 401,510 4/1889Muller 96ll6 1,896,567 2/1933 Trist 96l 16 1,995,958 3/1935 Bennett 96116 2,292,313 8/1942 Yule 96-116 NORMAN G. TORCHIN, Primary Examiner.

J. TRAVIS BROWN, Examiner.

R. H. SMITH, Assistant Examiner.

1. A CONTACT SCREEN COMPRISING A SUBSTANTIALLY TRANSPARENT SHEET AND ASURFACE LAYER ON SAID SHEET, SAID SURFACE LAYER INCLUDING A GRADUALLYVARYING GREY TONE PORTION EXTENDING FROM EACH OPAQUE DOT TOWARDS EACHPORTION EXTENDING FROM EACH OPAQUE DOT TOWARDS EACH DOT ADJACENTTHERETO, EACH GREY TONE PORTION DIMINISHING TO A MINIMUM OPACITY ZONEBETWEEN EACH OPAQUE DOT AND THE CORRESPONDING ADJACENT DOT, THE MINIMUMOPACITY ZONES SURROUNDING RESPECTIVE OF SAID OPAQUE DOTS, SAID SURFACELAYER FURTHER HAVING SEMI-TRANSPARENT ZONES DISTRIBUTED ABOUT THE OPAQUEDOTS AND LOCATED BETWEEN SAID MINIMUM OPACITY ZONES, SAID SURFACE LAYERFURTHER HAVING SUBSTANTIALLY FULLY TRANSPARENT SPOTS LOCATED IN THESEMI-TRANSPARENT ZONES, SAID SEMI-TRANSPARENT ZONES HAVING ABOUT .5 TO5% THE OPACITY OF SAID OPAQUE DOTS, THE AREA OF EACH TRANSPARENT SPOT TOTHE AREA OF THE ASSOCIATED SEMI-TRANSPARENT ZONE BEING ABOUT 1:20 TO1:60.